Vehicles driven by an internal combustion engine having a torque converter and an automatic transmission have used a torque sensor. The output of the torque sensor can be used to control engine or transmission performance. A number of approaches have been proposed for utilizing the engine torque sensor signal to achieve improved powertrain control. One such method is described in U.S. Pat. No. 5,319,555. Using the engine torque sensor output signal, vehicle driving resistance can be calculated with high precision. This information is then used to determine the most appropriate transmission gear ratio for various driving conditions such as hill climbing. In other words, transmission performance can be improved by using the output signal of the engine torque sensor.
The inventors herein have recognized a disadvantage with this approach. A typical torque sensor is usually a piezoelectric or a magnetostrictive device, which has a tendency to drift under certain operating conditions. For example, changes in ambient temperature may cause errors in the output signal values. Such errors are especially significant near very low engine torque levels such as those experienced in idle conditions. These errors lead to degraded engine control and cause reduced fuel economy and degradation in drive feel and vehicle performance. In other words, when the output signal of the engine torque sensor is not representative of the actual engine torque, engine performance optimization is degraded.